Condensing water heater with dielectrically insulated secondary flue

ABSTRACT

A high efficiency condensing flue gas-fired water heater is provided with a secondary tubular flue mounted inside the water tank and secured thereto by dielectric connectors to electrically isolate the secondary tubular flue from the tank. The secondary tubular flue has an intermediate helical section and opposed connecting end sections which each form a part of the dielectric connectors. The connectors do not require any welding for its installation to the tank and a compression nut and dielectric insulators provide for a leak proof and electrically isolated connection. The method of securing the secondary tubular flue is also described.

TECHNICAL FIELD

The present invention relates to condensing flue water heaters, andparticularly to a condensing flue water heater wherein a dielectricallyinsulated secondary flue is mounted inside the water holding tank of thewater heater.

BACKGROUND OF THE INVENTION

Gas-fired, condensing water heater manufacturers, continuously strive toincrease the efficiency of the water heater, that is to say thepercentage of the combustion energy which is transferred to the waterbeing heated in the tank. Such water heaters produce condensation andthe heat released by the water vapor is relatively high and a largeamount of energy of combustion is contained therein. By condensing thishot water vapor to exchange its heat with the water, the thermalefficiency of the water heater can be increased in the order of at least90%.

One method of increasing the efficiency has been to capture the hotgases leaving the flue of the water heater and recycling these in anexternal heat exchanger to heat water to be fed back to the tank of thewater heater or to use it for other purposes.

More recently some fabricators have constructed water heaters whereinthe flue is extended to make a second pass into the tank for heatexchange with the water being heated and thereby increasing theefficiency. An example of such design can be found in U.S. Pat. No.7,836,856 wherein it is stated that 80% of the heat from the combustiongases is transferred to the water within the water tank through the wallof the central flue without condensation, and an additional 10% or moreof the combustion heat is transferred to the water accompanied bycondensation of water in a coiled flue section which is welded to thetop end of the central flue which is closed. The coil is supported byconnecting rods which are welded to the base and the coil whereby todispose the coil about the central flue at a downward angle to evacuatethe condensation liquid. The bottom end of the coil exits the tankthrough a hole and welded thereabout. The installation of such anassembly is difficult and different type metal come into contact insidethe tank and this would result in early deterioration of the sacrificialanode which is mounted in the tank to prevent corrosion of the submergedexposed metal leading to lower tank life.

Another example of such designs is disclosed in U.S. Pat. No. 7,992,526wherein the central flue exits the top wall of the tank and the hotgases are fed back by a blower mounted on the top wall, into a secondpass straight flue conduit, of fairly large diameter, extending throughthe top wall and extending into the tank to exit the tank at a lowerside end thereof. Both flue conduits can be fitted with baffles toincrease its efficiency and such baffles are well known in the art. Theinstallation of the second pass flue requires the cutting of large holesin the tank wall to position the top and bottom end of the second passflue and thereafter welds have to be made to seal the gaps between thesecond pass flue and the tank wall. Because of the large diameter of thesecond pass flue, the size of the holes need to be fairly large and ofoblong shape to permit the flue ends to be fished there throughresulting in difficult weld seams which could develop leaks and thesewelds create a different metal exposure to the inside of the tank andthus increasing further deterioration of the sacrificial anode causingit to be consumed earlier which results in the formation of corrosioninside the tank and a reduction in the life span of the water heater.The assembly of such water heaters is also difficult and more costlyalthough they yield an efficiency exceeding 90%.

SUMMARY OF THE INVENTION

It is a feature of the present invention to provide a condensing fluewater heater fitted with a secondary tubular flue mounted inside thetank and which overcomes the above mentioned disadvantages of knowncondensing flue water heaters such as those described above.

Another feature of the present invention is to provide a condensing fluewater heater wherein the secondary tubular flue is connected to the tankwall by dielectric connectors and which do not require any welding tothe tank wall.

A still further feature of the present invention is to provide acondensing flue water heater wherein the secondary tubular flueconnectors are self sealing by an external bolt connection.

Another feature of the present invention is to provide a condensing fluewater heater wherein the dielectric connectors preserve the integrity ofthe tank as compared to weld connections.

Another feature of the present invention is to provide a condensing fluewater heater wherein the secondary tubular flue is secured inside thetank independent from the tank walls and thus maintaining the tank andthe glass lining integrity.

A still further feature of the present invention is to provide acondensing flue water heater wherein the thermal efficiency of the waterheater is increased up to about 99%.

A further feature of the present invention is to provide a condensingflue water heater wherein a baffle plate may be disposed inside the tankto stratify the bottom portion of the tank in a colder water zone wherethe helical section of the secondary flue is disposed to increase thedifferential in temperature between the flue gases in the helicalsection with the surrounding water temperature.

A further feature of the present invention is to provide a condensingflue water heater provided with a secondary flue coupled to the primaryflue and mounted inside the water holding tank of an up-fired ordown-fired condensing water heater.

A still further feature of the present invention is to provide asecondary tubular flue adapted to be mounted to a tank wall bydielectric connectors which are entirely securable from outside the tankwall.

Another feature of the present invention is to provide a method ofsecuring a secondary tubular flue in a water holding tank of a bottomfired water heater which is simple, economical and which does notrequire the formation of welds.

According to the above features, from a broad aspect, the presentinvention provides a condensing flue water heater having a water holdingtank with a combustion chamber at a bottom end of the tank. At least onesacrificial anode is disposed in the water holding tank. A primary flueextends through the tank and communicates at a bottom end thereof withthe combustion chamber. The primary flue exits the top wall of the tankthrough an exit opening. A secondary tubular flue is disposed in thewater holding tank and has a helical section. The secondary tubular fluehas a top connecting end section adapted to form part of a topdielectric tank connector for securement in a hole formed in a wall in atop part of the tank. The secondary tubular flue has a bottom connectingend section adapted to form part of a bottom dielectric tank connectorfor securement in a hole formed in a side wall of the thank spaced abovethe combustion chamber. A flue connecting means interconnects the exitopening of the primary flue with a top opening of the secondary flue. Ablower displaces the combustion gas from the combustion chamber throughthe primary flue and the secondary tubular flue and through an exhaustpipe, to atmosphere.

According to another broad aspect of the present invention there isprovided a secondary tubular flue for connection in a water holding tankof a gas-fired water heater to increase the efficiency of the waterheater. The secondary tubular flue has opposed tubular end sections anda helical tubular section integrally formed. The tubular end sectionseach have connecting end sections adapted to form a part of a dielectrictank connector for securing the secondary tubular flue inside the waterholding tank by the dielectric connectors.

According to a still further broad aspect of the present invention thereis provided a method of securing a secondary tubular flue in a waterholding tank of a bottom-fired water heater. The method comprises thesteps of providing a secondary tubular flue conduit having opposedstraight tubular end sections and a helical section integrally formed.The tubular end sections each have a pressure flange immovably securedtransversely thereabout and spaced a predetermined distance from a freeend thereof. A dielectric gasket is positioned about the free ends ofthe opposed straight tubular end sections to abut against an outersurface of the pressure flange. The secondary flue is inserted from abottom open end of the water holding tank prior to installing a bottomwall of the water holding tank with the bottom wall having a straightcentral flue secured thereto. An upper one of the opposed straighttubular sections is positioned in a hole formed in a top end section ofthe water holding tank and a lower one of the opposed straight tubularsection is positioned in a hole formed in a side wall of the waterholding tank spaced a predetermined distance from the bottom wall of thetank to be later installed. The dielectric tank connector is assembledonto an end section of each of the straight tubular end sections toconnect the tubular end sections to the tank by an electricallyinsulated and leak proof connection.

According to a further broad aspect of the present invention there isprovided a method of securing a secondary tubular flue in a waterholding tank of a bottom-fired gas water heater. The method comprisesproviding a secondary tubular flue conduit having opposed straighttubular end sections and an intermediate helical section integrallyformed. The tubular end sections each have a threaded connecting endportion extending from an end opening thereof. The secondary tubularflue is inserted from a bottom open end of the water holding tank priorto installing a bottom wall of the water holding tank with the bottomwall having a straight central flue secured thereto. An upper one of theopposed straight tubular section is positioned in a hole formed in a topend section of the water holding tank and a lower one of the opposedstraight tubular section in a hole formed in a side wall of the waterholding tank spaced a predetermined distance from the bottom wall of thetank. The dielectric tank connectors are assembled onto the threadedconnecting end portion of each of the straight tubular end sections toconnect the tubular end sections to a metal ring immovably secured aboutan outer surface of the water holding tank about the hole to provide anelectrically insulated and leak proof connection.

According to a further broad aspect of the present invention thesecondary tubular flue is mounted in a water holding tank of adown-fired gas water heater. The water heater has at least onesacrificial anode disposed in the water holding tank. A primary flueextend in the tank and communicates at a top end thereof with thecombustion chamber and at a bottom end with a secondary tubular fluedisposed in the water holding tank. The secondary flue has a helicalsection disposed about the primary flue. The secondary tubular flue hasa top connecting end section adapted to form part of a top dielectricconnector for securement to the bottom end of the primary flue insidethe tank. The secondary tubular flue has a bottom connecting end sectionadapted to form part of a bottom dielectric tank connector forsecurement in an exit hole formed in a side wall of the water holdingtank spaced above a bottom wall of the water holding tank. A blowerdisplaces the combustion gas from the combustion chamber through theprimary flue and the secondary tubular flue and through an exhaust pipeconnected to the bottom connecting end section outside the exit hole toexhaust cooled flue gas to atmosphere

DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be describedwith reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a bottom-fired gas water heater equippedwith the secondary tubular flue of the present invention mounted insidethe water holding tank which is housed in the outer shell shown herein;

FIG. 2 is a perspective view, partly fragmented, which illustrates basicparts of the construction of a bottom-fired gas water heater constructedin accordance with the present invention;

FIG. 3 is a side view, partly sectioned and fragmented, to illustrate anexample of the construction of the dielectric connector for securing theend sections of the secondary tubular flue to the tank walls;

FIG. 4A is a simplified side view showing an alternative design for theprovision of the pressure flange and wherein a casted fitting is weldedto straight ends of the secondary tubular flue:

FIG. 4B is a fragmented end view of an end section of the secondarytubular flue showing a modification for mounting the lock nut thereto;

FIG. 5A is a perspective view illustrating an example of theconstruction of the secondary tubular flue of the present invention;

FIG. 5B is a side view of FIG. 5A,

FIG. 6 is a side view, partly sectioned and fragmented, to illustrate afurther example of the construction of the dielectric connector forsecuring the end sections of the secondary tubular flue to the tankwalls;

FIG. 7 is a fragmented front view showing the outer metal ring welded tothe outer surface of the water holding tank wall;

FIG. 8 is an exploded perspective view of the water holding tank and thesecondary tubular flue and its dielectric connector parts:

FIG. 9 is a simplified, partly sectioned and fragmented view showing theblower mounted on the top wall of the outer shell of the water heaterbetween the central primary flue and the inlet of the secondary tubularflue and blowing down through the secondary flue, and,

FIG. 10 is a simplified side sectional view of a down-fired water heaterin which is mounted the secondary tubular flue of the present inventionwith its dielectric connections.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, and particularly to FIGS. 1 and 2, thereis shown generally at 10 a bottom-fired gas water heater fitted with thesecondary tubular flue 11 of the present invention mounted inside thewater holding tank 12. As herein shown a blower 13 is mounted on the topwall 14 of the outer shell 15 of the water heater and connected to anexhaust flue pipe 52 through which exhaust flue gases from the bottom ofthe secondary tubular flue are drawn and exhausted to the atmosphere. Acontrol 18 operates the burner 19 which is positioned in the combustionchamber 20.

With additional FIG. 2, there is shown details of the construction ofthe condensing flue water heater of the present invention. As shown inFIG. 2, the water holding tank 12 has a bottom wall 21 which defines thetop wall of the combustion chamber 20 which is in contact with the waterin the water holding tank. A central primary flue 22 extends through thetank and communicates at a bottom end through a central hole 23 (seeFIG. 8) in the bottom wall 21 with the combustion chamber. The top end24 of the primary central flue 22 exits the top wall 12′ of the tankthrough a hole 25. A flue connector 16, formed of suitable metal orplastics material, links the top end of the primary flue 22 to thesecondary tubular flue 11 to channel the hot gases therein. A fluebaffle assembly 26 equipped with damper plates 27 is disposed inside theprimary central flue to increase the travel path of the hot exhaustgases and create turbulence to improve heat transfer to the watercontained in the water holding tank. Such baffle assemblies are wellknown in the art. One or more sacrificial anode rods 9 are connected tothe top wall 12′ of the tank and extends therein spaced from allinternal components inside the tank to prevent corrosion of exposedmetal by being consumed in place of the exposed metal it is protecting.A dip tube 28 conducts the domestic water supply to the bottom end ofthe water holding tank.

With reference to the additional FIGS. 3 to 5B, the secondary tubularflue 11 of the present invention is comprised of a flue conduit shapedto have a helical tubular section 29 disposed between a substantiallystraight opposed sections 30 and 31, and which is better illustrated inFIGS. 5A and 5B. The flue conduit 11 may be formed from regular straightwall tubing, corrugated metal tube or fin tube or other known suitabletubing to improve heat exchange with the water contained in the tank.The helical tubular section 29 has its coil windings 29′ inclined at adownward angle, as better seen in FIG. 5B, to evacuate condensationformed therein towards the bottom section 31 which is also downwardlyinclined. These straight sections 30 and 31 each have straightconnecting end sections 30′ and 31′ which form part of a respectivedielectric tank connector for securement in a respective hole formed inthe top wall 12′ and a lower end of the side wall 12″ of the tank 12above the combustion chamber 20. The straight connecting end sections30′ and 31′ each have a pressure flange 32 immovably securedtransversely thereabout by welding or brazing or other suitable means.These pressure flanges 32 are spaced a predetermined distance from theend openings 33 of the connecting end sections 30′ and 31′. The pressureflanges 32 form an inner part of their respective dielectric tankconnectors. The purpose of the dielectric tank connectors is toelectrically insulate the secondary tubular flue 11 from the tank wallto make the secondary tubular flue 11 independent from the tank. Also,the dielectric tank connectors, as will be described further on, do notrequire any welding to the tank wall for their securement thereto andprovide a dielectric and water-tight seal about the holes formed in thetank wall through which the connecting end sections 30′ and 31′protrude. As previously mentioned, these connectors preserve theintegrity of the tank in contrast to a welded connection that would drawprotection from the sacrificial anode rod and by default reduce the lifeexpectancy of the water heater. Because the interior of these tanks arepre-glassed lined before the secondary tubular flue is installed,welding with the glass lining could lead to cracks in the glass coatingand coating burn-off which would also lead to lower tank life. Also,welding is a longer process and requires certified welders. Thesecondary tubular flue 11 may be fabricated from stainless steel,copper-nickel, or as a glass lined steel pipe. Other suitable metals arealso contemplated.

The entire construction of a first example of the dielectric endconnectors 35 is illustrated in FIG. 3. These dielectric end connectors35 are identical at opposed ends of the secondary tubular flue 11 andonly the lower one is described herein. The dielectric connector 35 iscomprised of a dielectric and water tight/resistant material annularflat gasket 36 which is fitted over the connecting end sections 30′ and31′ from the end opening 33 thereof and slid against an outer face 32′of the pressure flange 32 whereby to electrically isolate the pressureflange 32 from the inner surface 37 of the tank when the pressure flangeis biased under pressure against the inner surface 37 of the tank walland forms a water-tight seal about the hole 40 formed in the tank wallin the upper section and lower section of the tank.

The dielectric connector 35 has an outer portion which is comprised ofan outer metal ring 38 which is welded, as indicated by referencenumeral 39 or otherwise immovably secured to the outer surface 37′ ofthe tank wall 12″ and extends partly in the hole 40 formed therein forthe passage of the connecting end section 31′. A sleeve 43 formed ofelectrically insulating material, such as a phenolic-like substancecapable of resisting to the temperature of the flue conduit, is disposedover the connecting end section 30′ and fitted under the outer metalring 38 to electrically insulate the connecting end section from themetal ring 38 and hence the tank wall 12″. The sleeve extends the entirelength under the outer metal ring. The free end section of theconnecting end sections 30′ and 31′ is also provided with a connectionmeans in the form of a threaded section 41 formed on the outer surfaceof the free end section. A locking member in the form of a compressionnut 42 is threadably engaged with the threaded section 41. Beforeinstalling the compression nut 42 a further dielectric washer 43′ ispositioned about the connecting end section 31′ and slid against theouter face of the metal ring 38 to electrically isolate the compressionnut, which is in contact with the connecting end section 31′ of thesecondary tubular flue, from the outer metal ring which is in contactwith the tank wall. By threading the compression nut 42 over thethreaded section 41 and against the outer face of the outer metal ring,a pulling force is applied to the pressure flange 32 which in turnapplies a compression force against the dielectric/water tight and/orsealing gasket 36 disposed between the outer face of the pressure flangeand the inner surface 37 of the tank wall to provide a leak proof andelectrically isolated connection about the hole 40. The pressure of thewater within the tank also applies a compression force against thepressure flange.

FIG. 4A illustrates another example of the construction of theconnection of the pressure flange 32 to the secondary tubular flue. Asherein shown, the flange 23 is incorporated in a casted fitting 100 ofnon-corrosive metal, such as copper-nickel alloy, and which has atubular threaded extension 101 to form the connecting end sections 30′and 31′. The flange is a circumferential flat flange as previouslydescribed and a straight transverse end 102 of the tube is welded, witha like metal, about the hole formed in the flange and aligned with thetubular threaded extension. The fitting 100 may be disposed inwards ofthe tank or outwards thereof, and wherein in the later case the weldwould be performed outwards with the end sections 30′ and 31′ projectingout of the tank wall through its respective hole.

FIG. 4B illustrates an alternative to the formation of threads on theouter surface at the free end portion of the connecting end sections 30′and 31′, this alternative is to secure a sleeve 45 having an outerthreaded surface 46 about unthreaded connecting end sections of thesecondary tubular flue. The sleeve is welded or brazed over the free endof the connecting sections 30′ and 31′ to receive the lock nut inthreaded engagement therewith. This also solidifies the connecting endsections.

As shown in FIGS. 2 and 3, a variable diameter pipe coupling 50 formedof flexible material or other suitable material, interconnects the endsection of the connecting end section 31′ of the secondary tubular flue11 to a drain trap 51 secured at a bottom end of an exhaust pipe 52 toevacuate condensation. The hot gases which have been cooled leave thesecondary tubular flue at a temperature of about 110 to 125 degrees F.The hot gases are aspired by the blower 13 connected to the top end 52′of the exhaust pipe 52. The exhaust pipe and condensate trap are formedof suitable plastics material well known in the art.

With reference now to FIGS. 5A, and 5B, it can be observed that thesecondary tubular flue 30 is formed with the intermediate tubularhelical section 29′ disposed in a coil winding arrangement locatedsubstantially in a bottom third portion of the secondary tubular flue.With this configuration the helical section 29′ can be located in thebottom portion of the tank where the water is the coldest whereby toprovide for a greater delta-T, differential in the temperature betweenthe water in the water holding tank and the hot exhaust gases flowingthrough the helical section to thereby increase the thermal efficiencyof the water heater.

The secondary tubular flue 11 of the present invention with itsdielectric connectors provide for an ease in assembly with precisepositioning in a water holding tank of a bottom-fired gas water heater.The tank is provided with holes for the passage and connection of theopposed straight tubular sections 30′ and 31′ of the secondary tubularflue. The tank inner surface is glass lined before assembly of itsinternal components. In the assembly, the dielectric material flatannular gasket 36 is installed against the outer face 32′ of thepressure flange 32. The secondary tubular flue is then inserted from thebottom open end of the tank and the upper one of the opposed straighttubular section is positioned in the hole formed in the top wall of thetank. The lower one of the opposed straight tubular section is insertedin a hole formed in the side wall 12″ of the tank spaced above a bottomwall. The dielectric connectors 35 are then assembled and thecompression nut 42 tightened to provide for the gasket 36 to becompressed against the inner surface of the tank wall about the hole bythe flange 32 to provide the dielectric insulated connection and a leakproof seal. The gasket 36 has a predetermined thickness to besufficiently compressed to produce the leak proof seal. The securementof the connectors also automatically positions the helical tubularsection at a precise location within the tank to receive the centralflue of the bottom wall 21 of the tank at the center thereof.Essentially, the assembly is very simple, quick and no welding isrequired to secure the secondary tubular flue to the tank wall.

Referring now to FIG. 9, there is shown a further modification of thewater heater of the present invention wherein the blower is mounted onthe top wall 14 of the outer shell 15 and interconnects to the top end24 of the primary central flue 22 to the connector 35 of the secondarytubular flue secured to the top wall 12′ of the water holding tank 12.The blower draws the hot gases from the combustion chamber 20, throughthe central flue and redirects the hot gases into the secondary tubularflue 11, as shown by the arrows, and out to atmosphere through anexhaust flue pipe.

Referring now to FIGS. 6 to 8, there is shown another example of theconstruction of the connecting end sections 30′ and 31′ of the secondarytubular flue 11. Has herein shown, the connecting sections do not havethe pressure flanges 32 and therefore the dielectric connectors do nothave an internal portion. The end portions of the secondary tubular flueare simply threaded end portions 65 and 65′. These end portions aresimply positioned through their respective holes formed in the tank topwall 12′ and the lower end of the side wall, as previously described.FIG. 6 illustrates the construction of this alternative dielectric tankconnector 70 and seeing that this connector is the same at both ends ofthe secondary tubular flue, only the lower one is described herein.

The dielectric tank connector 70 is assembled and secured entirely fromoutside the tank and there are no internal parts, making the assemblypractically fool-proof. As with the previously described dielectricconnector 35, there is a locking ring 71 welded or braised to the outersurface of the tank walls about the holes 40 as shown by weld bead 73.The locking ring 71 is a thick circular annular metal ring having acentral bore 72 dimensioned to receive the connecting end sections 30′and 31′ of the secondary tubular flue. The ring also has an inner collarportion 74 which is closely fitted inside the hole 40, see FIG. 6.Threaded bores 75 are also machined in the flat outer face 76 of thelocking ring 71.

The dielectric tank connector 70 is comprised of a dielectricallyinsulated waterproof locking assembly 77 mounted on the threadedconnecting end portions 65 and 65′. A dielectric sleeve 78 is disposedabout the threaded connecting end portion 65′ and slid between the innersurface 71′ of the ring 71 and about the end section of the lowerstraight tubular section 31 to electrically isolate the ring 71, andhence the tank wall, from the tubular section 31. A water-tight flatdielectrically insulating annular compressable and deformable gasket 79is then positioned in close friction fit on the connecting end section65′ and slid over the outer face 76 of the locking ring 71. Anelectrically isolated annular mounting flange 80 is then threadably anddisplaceably engaged about the threaded end portion 65′ until it abutsagainst the seal gasket 79 with holes formed in the mounting flangealigned with the threaded bores 75 formed in the locking ring 71. Inthis example the mounting flange 80 is formed on non-conductive materialsuch as plastics. Bolts 81 are then disposed in the holes of the flange80 and screwed into the threaded through bores 75. This compresses theseal gasket 79 to deform and squeeze against the threaded end portion65′ forming a leak proof and dielectric seal. When the bolts 81 compressthe seal gasket 79 the threaded end portion 65′ is displaced a minordistance inside the tank. The seal gasket 79 may have a bead annularformation about its circular central opening to provide more sealingmaterial above the threaded end portion 65′

If the mounting flange 80 is constructed of metal, bushings 82 aredisposed in the holes formed in the flange 80. Also, a dielectric gasket83 is fitted about the threaded end portion 65′ and pushed against theouter face of the flange 80 to electrically isolate the flange. Thenon-conductive flange is therefore the preferred mounting part. As canbe observed, the entire dielectric connector is on the outside of thetank wall.

FIG. 8 is an exploded view of the assembly and its installation waspreviously described with reference to the first dielectric connectorexample. The parts of the second dielectric connector 80 are shown inthis figure.

Referring now to FIG. 10, there is shown generally at 85 a down-firedwater heater wherein a power burner 86 is mounted at the top of thewater holding tank 87. The burner flame 88 projects inside the centralflue 89 in the top part thereof about which the water inside the tank isat its hottest temperature. Although not shown, but obvious to a personskilled in the art, the domestic cold water supply is introduced at thebottom of the tank 87 by suitable means such as a dip tube, not shown.Therefore, the coldest part of the water within the tank is at thebottom. As herein shown, the secondary tubular flue 11 of the presentinvention is mounted inside the tank through the bottom wall 90 of thetank 87 before the bottom wall is installed. The dielectric connectorscan be either of the connectors 35 or 70 previously described. Theinstallation may be performed by disposing in the helical coil section29 about the central flue 91 which is secured to the top wall 93 of thetank and depends therein. The end section 31 of the secondary flue ispositioned in the hole provided at the bottom end section of the sidewall 92 and secured thereto by the side connector 35/70 in a manner aspreviously described. The end section 30 is then positioned in the hole94 as the bottom wall 90 is fitted in position. To position the endsection 30 in the hole 94, one method is to position a straight woodpeg, not shown, in the bottom end of straight section to align the hole94 with the straight end section 30 which is caused to protrude throughthe hole as the bottom wall sits in position for welding. The bottomdielectric connector 35/70 is then secured. The gas transfer chamber 95is installed to direct the hot gases from the central flue 91 into thesecondary tubular flue 11.

The hot gases are pushed through the secondary flue 11 and out toatmosphere through an exhaust pipe 96. A condensate trap 97 is locatedat the bottom end of the exhaust pipe. As herein illustrated the hotgases leaving the central flue 91 enter the bottom end portion of thetank where the water is at its coldest temperature and thus providingthe maximum delta-T for heat exchange through the sections 30, 31 andthe coil 29 of the secondary tubular flue. A bottom plate 99 is securedacross the bottom end of the water heater forming a chamber 100 intowhich high temperature insulation is disposed to prevent heat loss.

It is within the ambit of the present invention to cover any obviousmodification or improvements of the preferred embodiment describedherein provided such falls within the scope of the appended claims.Accordingly, the invention is not limited to the specific details shownand described herein.

The invention claimed is:
 1. A condensing flue water heater comprising awater holding tank constructed of metal and having a glass-lined innersurface, a combustion chamber at a bottom end of said water holdingtank, at least one sacrificial anode disposed in said water holdingtank, a primary metal flue extending through said tank and communicatingat a bottom end thereof with said combustion chamber and exiting at atop wall of said water holding tank through an exit opening, a secondarytubular flue also formed of metal disposed in said water holding tankand having a helical section disposed substantially equidistantly spacedabout said primary metal flue, said secondary tubular flue having a topconnecting end section adapted to form part of a top dielectric tankconnector for securement in a hole formed in a wall in a top part ofsaid tank, said secondary tubular flue having a bottom connecting endsection adapted to form part of a bottom dielectric tank connector forsecurement in a hole formed in a side wall of said water holding tankspaced above said combustion chamber, flue connecting meansinterconnecting said exit opening of said primary flue with a topopening of said secondary flue, and a blower for the displacement ofcombustion gas from said combustion chamber through said primary flueand said secondary tubular flue and through an exhaust pipe toatmosphere, said top and bottom dielectric connectors each beingcomprised by a connecting end portion of said top end section and saidbottom end section of said secondary tubular flue dimensioned to projecta predetermined distance out of their respective hole formed in saidwall in said top part of said tank and said hole formed in said sidewall of said water holding tank, respectively; an insulating sleeve ofnon-conductive material about each said connecting end portion andextending through respective ones of said holes, a dielectricallyinsulating component assembly about said connecting end portions and incommunication between said connecting end portion and said tank wallabout said holes in said top part of said tank and said side wall ofsaid tank, and compression means engageable exteriorly of said waterholding tank for applying compression to said dielectrically insulatingcomponent assembly to form a dielectrically insulated water-tight sealbetween said connecting end portions and said tank about said holes. 2.The condensing flue water heater as claimed in claim 1 wherein saidsecondary tubular flue is one of a stainless steel and a glass-linedmetal tubular flue.
 3. The condensing flue water heater as claimed inclaim 1 wherein said connecting means is a sealed connecting flue ductmounted on a top wall of an outer shell of said water heater.
 4. Thecondensing flue water heater as claimed in claim 1 wherein said bloweris secured to an outer casing of said water heater and coupled to abottom opening of said secondary tubular flue to create a suction fromsaid bottom opening.
 5. The condensing flue water heater as claimed inclaim 4 wherein said blower is mounted on a top wall of an outer casingof said water heater and coupled to said bottom opening through saidexhaust duct.
 6. The condensing flue water heater as claimed in claim 1wherein said blower is mounted on a top wall of an outer casing of saidwater heater between said exit opening of said primary flue and a topopening of said secondary flue, said blower forming part of saidconnecting means.
 7. The condensing flue water heater as claimed inclaim 1 wherein said top and bottom connecting end sections of saidsecondary tubular flue is provided with a pressure flange immovablysecured transversely thereabout and spaced a predetermined distance froman end opening of said top and bottom connecting end sections of saidsecondary tubular flue, said pressure flange forming an inner part of arespective one of said top and bottom dielectric tank connectors.
 8. Thecondensing flue water heater as claimed in claim 7 wherein said pressureflange of each said top and bottom dielectric tank connectors isprovided with a dielectric material gasket fitted against an outer faceof said pressure flange to electrically isolate said free end sectionsof said secondary tubular flue from a wall of said water holding tank insaid top part thereof and said side wall of said tank when said top andbottom connecting end sections are disposed in their respective holes toposition said top and bottom openings outside said water holding tank.9. The condensing flue water heater as claimed in claim 8 wherein saiddielectric material gasket is an annular flat gasket having apredetermined thickness and opposed flat surfaces for abutment betweensaid outer face of said pressure flange and an inner surface of saidtank wall surrounding said holes.
 10. The condensing flue water heateras claimed in claim 8 wherein said dielectric tank connector has anouter portion comprised of a metal ring immovably secured about an outersurface of said water holding tank about said hole formed in said toppart of said water holding tank and said side wall of said water holdingtank, said compression means being a locking member engageable about aconnecting end portion extending from said end opening of said top endand bottom connecting end sections of said secondary flue fordisplaceable abutment against a dielectric washer disposed about saidend sections between said metal ring and said locking member, saidlocking member urging said pressure flange against said inner surface ofsaid tank wall to apply a compression force against said dielectricmaterial gasket disposed between said outer face of said pressure flangeand said inner surface of said tank wall about said respective holes toprovide a leak proof and electrically isolated connection.
 11. Thecondensing flue water heater as claimed in claim 10 wherein said metalring is a steel ring welded to said outer surface of said water holdingtank about said holes.
 12. The condensing flue water heater as claimedin claim 6 wherein said connecting end portion of said top end andbottom connecting end sections of said secondary tubular flue is athreaded end portion.
 13. The condensing flue water heater as claimed inclaim 12 wherein said locking member is a compression nut threadablyengaged and displaceable about said threaded end portion.
 14. Thecondensing flue water heater as claimed in claim 10 wherein saidconnecting end portion is constituted by a sleeve having an outerthreaded surface, said sleeve being immovably secured about saidconnecting end sections, said locking member being a compression nutthreadably engaged and displaceable about said threaded surface of saidsleeve.
 15. The condensing flue water heater as claimed in claim 10wherein said dielectrically insulating component assembly includes anelectrically insulated sleeve disposed about a portion of each said topand bottom connecting end sections and positioned under said metal ringto electrically insulate said top and bottom end sections from saidmetal ring.
 16. The condensing flue water heater as claimed in claim 15wherein said electrically insulated sleeve is dimensioned for close fitbetween said dielectric washer and said dielectric material gasket. 17.The condensing flue water heater as claimed in claim 8 wherein said topand bottom connecting end sections of said secondary tubular flue areeach further provided with a connecting end portion extending from anend opening thereof.
 18. The condensing flue water heater as claimed inclaim 17 wherein said connecting end portions are each constituted by anouter threaded section formed about at least an outer surface portion ofsaid connecting end section from said end opening thereof, saidcompression means being compressed by a compression applying lockingmember threadably displaceable about said outer threaded section. 19.The condensing flue water heater as claimed in claim 1 wherein saidhelical section of said secondary tubular flue is an intermediatesection disposed at a location between said top and bottom connectingend sections whereby to be disposed at a predetermined location aboutsaid primary flue, said primary flue being a straight verticalcylindrical flue pipe.
 20. The condensing flue water heater as claimedin claim 1 wherein said secondary tubular flue has a straight uppersection which extends vertically in said water holding tank with saidtop dielectric tank connector thereof being secured in said hole whichis formed in a top wall of said water holding tank, said intermediatehelical section being an inclined helical section slopping transverselydownwards from said straight upper section, and a straight downwardlyinclined lower section for directing condensation in said secondarytubular flue outwardly of said water holding tank with said bottomdielectric tank connector secured in said hole spaced a predetermineddistance above said combustion chamber.
 21. The condensing flue waterheater as claimed in claim 20 wherein said dielectric tank connectorsecured spaced above said combustion chamber of said water holding tankhas a pipe coupling secured to said connecting end section thereof forsecuring an exhaust pipe thereto, and a condensate drain trap providedat a bottom end of said exhaust pipe adjacent said pipe coupling toevacuate condensate fluid from said secondary tubular flue, said blowerbeing secured to said exhaust flue pipe.
 22. The condensing flue waterheater as claimed in claim 21 wherein said blower is mounted on a topwall of an outer casing of said condensing flue water heater.
 23. Thecondensing flue water heater as claimed in claim 20 wherein said top andbottom connecting end sections of said secondary tubular flueincorporates a fitting secured to said secondary tubular flue and havinga circumferential flat flange having a central hole about which saidsecondary tubular flue is welded, a tubular extension tube extends fromthe opposed side of said flange and has a hole therein aligned with saidcentral hole in said flange, said tubular extension having an outerthreaded end portion and being of a diameter adapted to extend throughsaid holes formed in said tank.
 24. The condensing flue water heater asclaimed in claim 1 wherein said primary flue is provided with internalbaffles to increase the travel path of said hot flue gases propagatingthereabout from said combustion chamber to said exit opening and drawnout by said blower.
 25. The condensing flue water heater as claimed inclaim 17 wherein said connecting end portion is a threaded connectingend portion.
 26. The condensing flue water heater as claimed in claim 25wherein said top and bottom dielectric tank connectors are respectivelycomprised of a metal ring immovably secured about an outer surface ofsaid water holding tank about said hole formed in said top part of saidwater holding tank and said side wall of said water holding tank, saiddielectrically insulating component assembly being threadably secured tosaid threaded connecting end portion.
 27. The condensing flue waterheater as claimed in claim 26 wherein said dielectrically insulatedcomponent assembly is comprised of a dielectric sleeve disposed aboutsaid connecting end section to isolate said connecting end section fromsaid tank wall about said hole and said metal ring, a water-tightdielectrically insulating annular gasket about said connecting endsection and a connecting face of said metal ring, and an electricallyisolated annular mounting flange threadably and displaceably engagedabout said connecting end section, and wherein said compression means isa pressure applying locking means for interconnecting said annularmounting flange with said connecting face of said metal ring andcompressing said insulating annular gasket.
 28. The condensing fluewater heater as claimed in claim 27 wherein said pressure applyinglocking means is constituted by pressure applying bolts extendingthrough mounting holes formed in said annular mounting flange and inthreaded engagement with threaded bores formed in said connecting faceand aligned with said mounting holes.
 29. The condensing flue waterheater as claimed in claim 27 wherein said electrically isolated annularmounting flange is formed from a non-electrically conducting material.30. The condensing flue water heater as claimed in claim 27 wherein saidelectrically isolated annular mounting flange is a metal flange,dielectric bushings fitted in said mounting holes of said annularmounting flange and an external dielectric flat annular gasket over anouter surface of said annular mounting flange at least in the area ofsaid mounting holes to electrically insulate said pressure applyingbolts from said connecting end portion of said secondary flue.
 31. Thecondensing flue water heater as claimed in claim 27 wherein saidelectrically isolated annular mounting flange is threadably anddisplaceably engaged on said connecting end section to a predetermineddistance from said end opening of said connecting end section andpositioned for abutment against said water-tight dielectric insulatingannular gasket, said pressure applying means compressing said annulargasket between said connecting face of said metal ring and an inner faceof said annular mounting flange while causing slight inward displacementof said connecting end section in said water holding tank.